CVE-2018-9539 in Android
Summary
by MITRE
In the ClearKey CAS descrambler, there is a possible use after free due to a race condition. This could lead to local escalation of privilege with no additional execution privileges needed. User interaction is not needed for exploitation. Product: Android. Versions: Android-8.0 Android-8.1 Android-9. Android ID: A-113027383
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Analysis
by VulDB Data Team • 04/13/2020
The vulnerability identified as CVE-2018-9539 represents a critical security flaw within the ClearKey Content Access System descrambler component of Android operating systems. This issue manifests as a use-after-free condition that arises from a race condition in the implementation of the ClearKey CAS functionality. The vulnerability affects Android versions 8.0, 8.1, and 9.0, indicating a widespread impact across multiple major Android releases. The ClearKey CAS system is responsible for handling digital rights management operations for media content, making this vulnerability particularly concerning for media processing and playback functionalities.
The technical root cause of this vulnerability stems from improper synchronization mechanisms within the ClearKey CAS implementation. When multiple threads or processes attempt to access shared memory resources simultaneously, the race condition creates a window where a memory allocation is freed while another process still holds a reference to it. This fundamental flaw in memory management allows for potential memory corruption that can be exploited to gain elevated privileges. The vulnerability operates at the kernel level within the Android media framework, specifically within the ClearKey CAS subsystem that manages content decryption and access control. The race condition occurs during the lifecycle management of memory objects used for content decryption operations, where proper locking mechanisms fail to prevent concurrent access patterns that lead to the premature deallocation of memory regions.
The operational impact of this vulnerability is severe as it enables local privilege escalation without requiring any additional execution privileges or user interaction for exploitation. This means that any application running on the device with standard user permissions could potentially leverage this flaw to gain root-level access to the Android system. The implications extend beyond simple privilege escalation as the attacker could then access all system resources, modify critical system files, install malicious applications, or extract sensitive user data. The lack of user interaction requirement makes this vulnerability particularly dangerous as it can be exploited automatically without any user awareness or consent. The vulnerability's presence in the ClearKey CAS system also means that it could affect media playback operations, streaming services, and any application that relies on Android's content protection mechanisms.
Mitigation strategies for this vulnerability should focus on immediate patch deployment through official Android security updates, as the issue was addressed through kernel-level fixes in subsequent Android releases. System administrators and device manufacturers should prioritize updating affected Android versions to the latest security patches. Additionally, implementing runtime monitoring and memory access validation can help detect anomalous behavior patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-416, which describes use-after-free conditions, and represents a classic example of how race conditions in concurrent programming can lead to critical security vulnerabilities. From an ATT&CK framework perspective, this vulnerability maps to privilege escalation techniques and could be categorized under T1068, which covers 'Exploitation for Privilege Escalation', and potentially T1059, 'Command and Scripting Interpreter', as exploitation may involve executing malicious code with elevated privileges. Organizations should also consider implementing application whitelisting and restricting unnecessary media processing capabilities to minimize the attack surface, while maintaining comprehensive logging and monitoring of system calls related to memory management and content access operations.